An important service quality issue in cellular communication systems is to provide complete and reliable radio coverage of the geographical area that is intended to be covered by the cellular communication system. Cellular communication systems are typically optimized prior to commercialization to give an as good radio coverage as possible. However, since surroundings within the coverage area may change with time, coverage may also change. Adjustments of antennas, beams and/or emission powers are used to continuously minimize areas having poor radio coverage, typically on a network level. These efforts have been quite successful and today, 3G networks (Third generation mobile networks) has reached and stabilized at a drop rate of around 0.7-1.0%.
Further improvements call for cell level trimming or re-planning, which is more expensive and tedious. Such functionality is often referred to as O&M systems (Operation & Maintenance). A commonly adopted view-point is that work aiming to decrease the drop rate even further requires a very large effort in relation to the potential improvements. Since the drop rate is at a fairly low level today, further drop rate combat therefore has been considered as less important for the network operators, since such measures would lead to high costs.
A typical approach for further improving radio coverage is to visit the equipment sites and cell areas and actually measure the radio conditions at different sites. However, since cells, at least in rural areas can be very large indeed, in some cases even up to 10 000 km2, it is naturally very time consuming and costly to cover such large areas manually when searching for areas of poor coverage.
However, a continued call drop combat has clear advantages. The problem is that most prior art coverage tuning is based on a resource-demanding “blind” search for poor coverage areas.
In the published U.S. patent application US 2005/0136911, an apparatus and method for mobile station-assisted optimization of a wireless network are disclosed. Mobile stations are equipped with GPS receivers and are therefore continuously aware of their position. Radio signal parameters are stored in the mobile station and reported to a coverage server in the core network together with corresponding position information. In particular, when communication links to the wireless network are dropped, the mobile station reports the position for such a drop. The information is compiled in the coverage server and poor coverage areas may be detected, as well as fault functioning mobile stations.
The solution of US 2005/0136911 gives at least theoretically a good overview of good and bad coverage areas. However, a number of severe drawbacks are present. The solution relies on the active action of mobile stations, which calls for updated mobile stations. In particular, to reach the top resolution, GPS receivers have to be provided in the mobile stations, which receivers increase the cost for each mobile station tremendously. This makes it practically impossible to introduce such equipment as standard equipment in mobile stations. Furthermore, the mobile station performs a large part of the processing, some of it operating continuously, which increases the battery consumption. The reporting of the position data and/or signal parameters requires additional radio transmissions, also leading to increased battery consumption. The radio transmissions also consume available resources in the radio interface, leading to less traffic capacity. Furthermore, since mobile stations vendors are not typically allied with operators, there are small possibilities for the operators to influence the mobile station vendors to provide suitable mobile stations. Since the radio interface is standardized, the proposed solution needs substantial standardization efforts. Moreover, the overall solution requires a substantial and costly systemization and access network implementation.
A general problem with the solution of US 2005/0136911 is thus that the coverage improvements are results entirely dependent of active operations performed mainly in the mobile stations.